With a rapid development of wireless communication technology, portable electronic devices, for example, mobile phones or tablet personal computers (PCs) have a display screen with a large size to browse webs, play games, movies, and so on. However, when a user controls the large-size display screen, there is usually an area where a finger is not accessible, especially the area where a thumb is not accessible. Additionally, some of control elements of applications on the display screen may be too small to operate easily, which will cause an inconvenient operation.